382 TYPHOID FEVEK 



to live for long periods and to multiply outside the human 

 body. The investigation of the prevalence of the typhoid 

 bacillus under saprophytic conditions is a matter of great 

 difficulty, as for its proper study the capacity of the organism 

 to multiply in the presence of other intestinal and putrefactive 

 organisms constitutes the essential problem. There is no doubt 

 that the bacillus can remain viable under such circumstances for 

 &pme days and it may be for weeks. The existence of carriers 

 ir^ all communities where typhoid fever occurs has, however, 

 thrown new light on the subject and has accounted for the 

 origin of many outbreaks otherwise obscure. There is now r 

 some doubt whether the prolonged viability of the typhoid 

 bacillus under saprophytic conditions plays such an important 

 part in the incidence of the disease as has hitherto been supposed. 

 In many cases survival outside the body for a considerable time 

 is an essential factor where a water or food supply becomes in- 

 fected with material derived from a carrier. At the present 

 time small outbreaks of the disease frequently originate in those 

 who are brought into domestic contact with carriers, and larger 

 epidemics originate when a carrier pollutes a water or especially 

 a milk supply. During such outbreaks secondary cases may 

 arise in persons infected not from the primary source but from 

 contact with patients primarily infected. It cannot be said, 

 however, that the seasonal incidence of typhoid fever has been 

 completely elucidated, and this is especially true of the isolated 

 cases occurring about the same time in large communities in 

 persons unconnected with each other and whose contact with a 

 carrier cannot be traced. In certain cases it has been supposed 

 that flies constitute a factor in the prevalence of the disease by 

 infecting food after having been in contact with garbage, but 

 the evidence here is unconvincing. 



The Serum Diagnosis of Typhoid Fever. This method of 

 diagnosis is based on the fact that living and actively motile 

 typhoid bacilli, if placed in the diluted serum of a patient 

 suffering from typhoid fever, within a very short time lose their 

 motility and become aggregated into clumps. 



The methods by which the test can be applied have already 

 been described (p. 119). 



(1) It will be there seen that the loss of motility and clumping 

 may be observed microscopically. If a preparation be made by 

 the method detailed (typhoid serum in a dilution of, say, 1 : 30 

 having been employed), and examined at once under the micro- 

 scope, the bacilli will usually be found actively motile, darting 

 about in all directions. In a short time, however, these move- 



